In an EPC disclosed in, for example, Non-Patent Document 1, which is a standard related to an E-UTRAN (this term will be described later; the same applies to other terms throughout this paragraph), Always-On in which each GW maintains a tunnel is assumed. Thus, resources of a core network are necessary for the number of bearers to be established by a UE, which is a mobile terminal or the like. For this reason, the establishment of a tunnel and the assignment of an IP address are performed every time transmission from the UE is performed when the tunnel of the core network is released, and thus there is a possibility that the IP address issued to the UE is changed every time. In addition, it is impossible to notify the UE of reception when the tunnel of the core network is released.
In the above paragraph, E-UTRAN is an abbreviation for an evolved universal mobile telecommunications system (UMTS) terrestrial radio access network and represents one scheme of a radio access network. EPC is an abbreviation for an evolved packet core and is one scheme of a core network in which various radio access systems or the like are accommodated. GW is an abbreviation for a gateway and is a node which connects different types of networks. Here, a node is a logical representation of an apparatus on a network. UE is an abbreviation for user equipment, and represents a mobile terminal, a radio terminal, or the like. In addition, a tunnel refers to a virtual communication line implemented using encapsulation or the like. Always-On refers to a continuous Internet protocol (IP) connection. A core network refers to a portion which does not depend upon radio access in an overall network system. A bearer refers to a logical packet transfer path established between nodes.
On the other hand, in a UMTS terrestrial radio access network (UTRAN), which is another scheme of a radio access network described in, for example, Non-Patent Literature 2, a gateway general packet radio service (GPRS) support node (GGSN) manages UEs and IP addresses in a fixed manner, thereby making it possible to provide means for establishing a tunnel triggered by reception of a packet addressed to the IP address of a UE. However, there is a problem in that the UEs and the IP addresses are managed in a fixed manner, and thus the GGSN available to the UE is limited and it is necessary to set association information of the target UE and the IP address in the GGSN in advance.